Poloidal and toroidal rotation of the main ions (${\mathrm{He}}^{2+}$) and the impurity ions (${\mathrm{C}}^{6+}$ and ${\mathrm{B}}^{5+}$) in H-mode helium plasmas have been measured via charge exchange recombination spectroscopy in the DIII-D tokamak. It was discovered that the main ion poloidal rotation is in the ion diamagnetic drift direction while the impurity ion rotation is in the electron diamagnetic drift direction, in qualitative agreement with the neoclassical theory. The deduced radial electric field in the edge is of the same negative-well shape regardless of which ion species is used, validating the fundamental nature of the electric field in L-H transition phenomenology.

We have investigated hysteresis and the return-point memory (RPM) property in deterministic cellular automata with avalanche dynamics. The RPM property reflects a partial ordering of metastable states, preserved by the dynamics. Recently, Sethna et al. [Phys. Rev. Lett. 70, 3347 (1993)] proved this behavior for a homogeneously driven system with static disorder. This Letter shows that the partial ordering and the RPM can be displayed as well by systems driven heterogeneously, as a result of its own evolution dynamics. In particular, we prove the RPM property for a deterministic 2D sandpile automaton driven at a central site.

Small angle neutron scattering experiments were performed to measure the structure factor S(q) for a binary fluid water/lutidine mixture imbibed inside porous Vycor glass at concentrations both near and away from critical. In both cases, the results can be interpreted as a combination of a lutidine-rich wetting layer coating the internal surfaces of Vycor and random single-phase domain growth with temperature. This result does not support the random field Ising model predictions for the phase separation behavior, but is in good agreement with theories based on pore confinement of the imbibed fluid mixture.

Monte Carlo simulations show that a system of hard, spherical particles with a short-ranged attractive interaction, can undergo a first-order transition from a dense to a more expanded solid phase with the same structure. This phase transition is analogous to the liquid-vapor transition in systems with longer-ranged attractive forces. In particular, the solid-solid transition terminates in a critical point. We argue that this phase transition should be experimentally observable in certain types of colloidal crystals.

Multilayer ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ film growth on weak-binding alkali substrates is investigated with a nonlocal density functional theory. Although ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ wets all substrates down to zero temperature, prewetting transitions are predicted to occur on Cs, Rb, and K. Emphasis is put on the role played by the Fermi statistics. Continuous wetting is recovered with increasing strength of substrate potential. The heat capacity and the magnetization of the films exhibits steps associated with the occupation of two-dimensional Fermi disks.

We present the first clear evidence of a shear induced hexagonal phase in a polyionic fluid in flow past a plane quartz surface. The dilute surfactant solution studied is viscoelastic due to the formation and entanglement of highly extended charged threadlike micelles many thousands of Å long, which are known to align along the flow direction under shear. Small-angle neutron diffraction data show that in the high shear region within a few tens of microns of the surface these micelles not only align, but form a remarkably well ordered hexagonal array separated by 370 Å, 8 times their 46 Å diameter.

A local analysis of a relaxed and reconstructed Au(511) surface is studied using the real space Green’s function approach. The equilibrium configuration of the Au(511) surface is obtained by simulated quenching using the ‘‘glue’’ many-body potential. We found that a pair of localized modes, associated with the step-edge chain, appears outside the bulk band. These modes propagate on the surface at an angle (∼43.9°) with respect to the edge chain. In addition, we find a gap mode associated with the ridge chain, and the low frequency surface modes shifted en masse toward even lower frequencies.

We present a first microscopic study of the state of a semiconductor surface, clean Ge(111), close to the bulk melting temperature. Both electronic states and ionic motion are fully treated via first-principles molecular dynamics. Results indicate a clear dynamical disordering, confined, however, to the first atomic bilayer. This region acquires a liquidlike diffusion, and is metallic. Lack of melting of the second and deeper bilayers, found to be in good quantitative agreement with recent x-ray data, indicates an incomplete wetting of the semiconducting solid by its own metallic melt. Previously conflicting data on Ge(111) are also reconciled within this picture.

We have studied uniaxially stressed Ge doped with Cu, a substitutional triple acceptor, by photoconductivity spectroscopy. We find that the ground state of this triple acceptor, normally accommodating three 1s holes, reconfigures into an atomic Li-like 1${\mathit{s}}^2$ 2${\mathit{s}}^1$ arrangement by the application of [100] stress. Above 4 kbar the first ionization potential reaches a constant value of 17.4 meV corresponding to the hole excitation from the now partially occupied 2s energy level. Excellent agreement was obtained between the experimental results and variational calculations.

The Coulomb 1/r interaction plays an important role in quantum wires. We study the interplay between this long-range interaction and impurity. For a single band quantum wire, we find that the transport properties are strongly modified. The linear conductance G is found to vanish with temperature as G∼exp[-ν${\ln }^{3/2}$(1/T)] and the current voltage characteristics acquires a thresholdlike behavior. The possible extension of the theory to the case of many-band quantum wires is discussed.

We consider the effect of a magnetic field fluctuating in space and time on the transport of independent charged particles in a two-dimensional random potential. The renormalization of the diffusion coefficient and the destruction of phase coherence by the magnetic field lead to a finite quantum correction to the electrical conductivity δσ at finite temperature T. Comparison of our result with the standard weak localization expression yields an unusual effective phase breaking rate 1/${\mathrm{\tau }}_{\mathrm{\phi }}$∼${\mathit{T}}^{1/3}$. Our results explain the recently observed phase breaking rate in a ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CuO}}_6$ compound, and furnish proof for the existence of gauge fields in these materials.

Evidence for electron localization in 2D at metal-dielectric interfaces is reported. A nondispersive peak, derived from the image-potential state and observed in angle-resolved two-photon photoemission, is assigned to localized excess electrons. The image electron on alkane monolayers is a free electron. Bilayers of chain or ring alkanes show both localized and delocalized states; electrons are localized on trilayer n-pentane. Bilayers and trilayers of neopentane show no localization. Our results link the geometry of adlayer molecules with localization of excess electrons at interfaces.

The magnetic properties of Fe-Pd multilayers are strongly affected by the high magnetic polarization of Pd. The origin of the magnetization of Pd in contact with Fe is examined. We found that a surface Pd(100) photoemission structure persists upon preparation of 1 and 2 monolayers Fe. Comparison with an ab initio calculation identifies this structure as a state distributed equally between the Fe and the adjacent Pd layer. Spin analysis of the photoelectrons shows that this state is magnetic, and the calculation reveals that it contributes to the large Pd moment at the interface of 0.32${\mathrm{\mu }}_{\mathit{B}}$.

We present direct measurements at room temperature of the conductance of a point contact between a scanning tunneling microscope tip and Ni, Cu, and Pt surfaces. As the contact is stretched the conductance jumps in units of 2${\mathit{e}}^2$/h. Atomistic simulations of the stretch of the contact combined with calculations of the conductance using the Landauer formula show that the observed behavior is due to the quantization of the transverse electron motion in a contact which contains between one and ten atoms.

We investigate the sliding state of a two-dimensional Wigner crystal in a strong magnetic field in the presence of randomness and free carriers, using a high-velocity perturbation theory. We find that the Hall resistivity retains its classical value within the second order Born approximation, and that disorder induces predominantly transverse distortions. We calculate the interference effects that arise in combined ac+dc fields for the present system. We examine recent experiments that measure the nonlinear conductivity for the insulating phases in the fractional quantum Hall effect regime.

The Hall effect of an ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ epitaxial film was studied using high pulsed current densities J to suppress flux pinning and reveal intrinsic behavior in the free-flux-flow limit. With increasing J there is an enhancement of the anomalous sign reversal, inconsistent with mechanisms based on pinning and inhomogeneity. At high H and J the Hall angle α appears to decompose into α=${\mathrm{\alpha }}_{\mathit{M}}$+${\mathrm{\alpha }}_{\mathit{n}}$: ${\mathrm{\alpha }}_{\mathit{M}}$(T) saturates to a negative value independent of H and J, and ${\mathrm{\alpha }}_{\mathit{n}}$ (∝H) has the normal-state value. The results are consistent with time-dependent Ginzburg-Landau calculations.

The surface impedance at 10 GHz was measured systematically in single-crystal ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ for carrier concentrations 0.09≤x≤0.19, from which penetration depth λ was determined. The anisotropy and the depencences on x and temperature T of λ are extensively studied for the first time. The anisotropy of λ(T=0) decreases with increasing x, and still remains larger than 10 for x=0.19. The out-of-plane penetration depth (${\lambda }_{\mathit{c}}$) has a different temperature dependence from the in-plane one (${\lambda }_{\mathit{a}\mathit{b}}$). These results suggest that the electrodynamic properties in the superconducting state along the c axis can be explained by a Josephson-coupled layer model.

Josephson tunneling currents have been observed on low leakage Pb/insulator/${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ tunnel junctions. The junctions are planar with tunneling into the c axis. We have studied these Josephson currents on junctions with resistances varying by more than 2 orders of magnitude. From the magnetic field modulation of the Josephson current, the low temperature value and the temperature dependence from 1.3 to 4.2 K of the c-axis penetration depth were measured. This observation of Josephson coupling along the c axis between a conventional superconductor (Pb) and a cuprate raises questions about the proposed d-wave nature of the superconducting order parameter in the cuprates.

We present internal friction (IF) measurements in magnetic fields up to 1.6 T of epitaxial ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ thin films with different thicknesses. Measurements at constant temperature and varying field exhibit peaks in the IF at particular values of the field for H perpendicular to the crystallographic c axis. Assuming a rectangular flux line arrangement and taking the anisotropy of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ into account the positions of the peaks coincide with fields where the distance in c direction of the flux line rows becomes an integral fraction of the sample thickness. This matching effect is valid for different film thicknesses and seems to be independnet of temperature.

We show that in a certain range of parameters the interaction between vortices causes significant enhancement of galvanomagnetic effects in thin superconducting films, as opposed to thick films. In particular, the Nernst coefficient acquires a contribution exceeding the single vortex term at relatively small external magnetic fields. The possibility of inducing the dc voltage due to either vortex-antivortex pair production by ac external currents or pair-breaking radiation is also discussed. Our results give a possible explanation for the experiments of A. Gerber and G. Deutcher.